Method an apparatus for asynchronously forming magnetic liquid droplets

ABSTRACT

Droplets of a magnetic liquid are pulled from an outlet or orifice of a nozzle by applying a magnetic force to the magnetic liquid, which is under a relatively low static pressure, within the nozzle whereby the droplets, which are ink, impinge upon a recording surface. Each droplet is pulled from the outlet of the nozzle by applying a magnetic force adjacent the outlet, a magnetic force from the opposite side of the recording surface from the nozzle outlet, or magnetic forces from both sides of the recording surface.

United States Patent [1 1 Fan et al.

[ Oct. 28, 1975 METHOD AN APPARATUS FOR ASYNCIIRONOUSLY FORMING MAGNETIC LIQUID DROPLETS [75] Inventors: George J. Fan, Ossining; Richard A.

Toupin, Briarcliff Manor, both of N.Y.

[73] Assignee: IBM Corporation, Armonk, N.Y.

[22] Filed: Feb. 27, 1974 [21] Appl. No.: 446,559

[52] US. Cl 346/1; 346/140 [51] Int. Cl. GOlD 15/16 [58] Field of Search 346/140, 75, l

[56] References Cited UNITED STATES PATENTS 3,787,879 1/1974 Ichioka et al. 346/140 3,805,272 4/1974 Fan et a1 346/140 X OTHER PUBLICATIONS Chen, W. I-I.; Magnetic Ink Jet Printer; IBM Tech.

Disc. Bulletin, Vol. 16, No. 6, November 1973, p. 1936.

Primary Examiner-Joseph W. Hartary Attorney, Agent, or Firm-Frank C. Leach, .Ir.

[5 7] ABSTRACT Droplets of a magnetic liquid are pulled from an outlet or orifice of a nozzle by applying a magnetic force to the magnetic liquid, which is under a relatively low static pressure, within the nozzle whereby the droplets, which are ink, impinge upon a recording surface. Each droplet is pulled from the outlet of the nozzle by applying a magnetic force adjacent the outlet, a magnetic force from the opposite side of the recording surface from the nozzle outlet, or magnetic forces from both sides of the recording surface.

15 Claims, 4 Drawing Figures GENERATOR 1B PULSE M I US. Patent Oct. 28, 1975 3,916,419

I FIG.1A

/|NK RESERVOIR 10 PULSE GENERATOR FIG.2

F DELAY L 28 F PULSE f Rm METHOD AN APPARATUS FOR ASYNCIIRONOUSLY FORMING MAGNETIC LIQUID DROPLETS Printing on a recording surface can be accomplished by asynchronously directing ink droplets to the recording surface when printing is to occur in accordance with a desired pattern. Thus, printing occurs without any contact with the recording surface other than the droplet of ink engaging the recording surface.

One means of asynchronously applying the droplets of ink to a recoritling surface has utilized an ink chamber in which the chamber has been mechanically deformed whenever it is desired for a' droplet of ink to be applied to the recording surface in accordance with the pattern to be written thereon. The mechanical deformation of the ink chamber changes its volume to cause a droplet of ink to squirt from the chamber onto the paper from the nozzle of the chamber.

The chamber has a resonant frequency beyond which the chamber does not respond to mechanical deformation. Thus, the speed with which the droplets of ink can be applied to the recording surface when using mechanical deformation of the ink chamber has been limited because of the resonant frequency.

Furthermore, to produce the desired mechanical deformation of the ink chamber to change its volume to squirt a droplet of ink therefrom has required a relatively large quantity of energy. Thus, the mechanical deformation of the ink chamber for asynchronously applying ink droplets to a recording surface has not been an efficient means of producing ink droplets.

The present invention satisfactorily solves the foregoing problems through eliminating the requirement for any mechanical force to cause asynchronous application of ink droplets on a recording surface. The present invention does not require any deformation of an ink chamber.

The present invention uses the application of magnetic force on a magnetic liquid to pull each droplet from the nozzle outlet or orifice. Thus, while a magnetic liquid must be employed with the present invention, the problems inherent with the mechanical deformation system are eliminated by the present invention.

In the present invention, the magnetic force applied on the magnetic liquid, which is maintained under a very low static pressure, must be sufficient to overcome the force produced by the surface tension, which holds the magnetic liquid within the nozzle. By applying a relatively large magnetic force on the magnetic liquid in comparison with the surface tension force, a droplet of the magnetic liquid can be pulled out of the nozzle outletfor application to a recording surface.

An object of this invention is to asynchronously form magnetic liquid droplets.

Another object of this invention is to provide asynchronous application of magnetic ink droplets to a recording surface.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawing.

In the drawing:

FIG. IA is a schematic side elevational view, partly in section, of an ink recording arrangement having one embodiment of the magnetic force applying means of the present invention for forming the droplets for application to the recording surface.

FIG. 1B is an end elevational view of the structure of FIG. 1A and taken substantially along line 1B1B of FIG. 1A.

FIG. 2 is a side elevational view, partly in section, showing another arrangement of the present invention for applying a magnetic force to form a droplet for application on the recording surface.

FIG. 3 is a fragmentary side elevational view showing magnetic fields applied from both sides of a recording surface to form a droplet for application on the recording surface.

Referring to the drawing and particularly FIG. 1A, there is shown an ink resevoir 10 of magnetic ink. One suitable example of the magnetic ink is a ferrofluid of the type described in our copending patent application for Recording System Utilizing Magnetic Deflection, Ser. No. 284,822, filed Aug. 30, 1972, now U.S. Pat. No. 3,805,272 and assigned to the same assignee as the assignee of this application. Another example of magnetic ink is a stable colloidal suspension in water of 100 A size particles of magnetite (Fe;,O,) with surfactant surrounding the particles.

The ink reservoir 10 communicates with a nozzle 11 having an outlet or orifice 12 of relatively small diameter. The magnetic liquid is maintained within the nozzle 11 under a relatively low static pressure such as several inches of water, for example. This pressure is not sufficient to cause the magnetic liquid to be expelled through the outlet or orifice 12 of the nozzle 11. The surface tension of the magnetic liquid is sufficient to retain the magnetic liquid within the outlet or orifice 12 of the nozzle 11 when the magnetic liquid has a relatively low static pressure applied thereto.

A C-shaped magnet 14 (see FIG. 1B) is disposed adjacent the nozzle outlet or orifice 12 as shown in FIG. 1A. The magnet 14 has its pole faces 15 and 16 tapered to form a reducing gap therebetween adjacent the outlet or orifice 12 of the nozzle 11. One of the pole faces 15 and 16 is a north pole, and the other of the pole faces 15 and 16 is a south pole. The tapered pole faces 15 and 16 produce a relatively large magnetic force.

The magnet 14 has a plurality of windings of a coil 17 wrapped therearound as shown in FIG. 1B. The ends of the coil 17 are connected to a pulse generator 18,

which supplies a current to the coil 17 when it is desired to exert a magnetic force on the magnetic liquid within the nozzle 11 to pull a droplet 19 from the outlet or orifice 12 of the nozzle 11 for impingement on a recording surface such as a paper 20, which is moving vertically relative to the outlet or orifice 12 of the nozzle 11 as shown in FIG. 1A.

The droplet 19 is attracted to the narrowest portion of the gap between the pole faces 15 and 16 of the magnet 14. The tapering of the pole faces 15 and 16 creates a magnetic force gradient with the gradient being zero adjacent the tips of the pole faces 15 and 16 and the strength of the field being a maximum at the tips.

Since the non-uniform gradient created by the tapered pole faces 15 and 16 of the magnet 14 changes the direction in which the magnetic force is applied to the magnetic liquid shortly after the droplet 19 passes the tips of the pole faces 15 and 16 of the magnet 14, it is necessary for the recording surface 20 to be very close to the tips of the pole faces 15 and 16 of the magnet 14. Otherwise, instabiliity of the motion of the droplet 19 will occur. Thus, the recording surface 20 must be closer to the tips of the pole faces 15 and 16 of the magnet 14 than the narrowest width of the gap between the pole faces 15 and 16.

Accordingly, whenever the pulse generator 18 supplies a current to the coil 17, a non-uniform magnetic force gradient is applied to the magnetic liquid within the nozzle 11 to pull one of the droplets 19 from the outlet or orifice 12 of the nozzle 11 for impingement on the paper 20. As a result, the droplets 19 can be asynchronously produced for application to the recording surface 20 in accordance with the desired pattern since the pulse generator 18 is energized in accordance with the pattern and the rate of movement of the paper 20.

An example of how the magnetic force applied to the magnetic liquid is sufficient to pull the droplet 19 from the outlet or orifice 12 of the nozzle 11 when the outlet or orifice 12 has a diameter of 2 mils will be given. The magnetic force on the magnetic liquid is equal to the product of the magnetic moment and the field gradient. If the magnetic moment is approximately 30 emu/gram and the field gradient is 10 gauss/cm, then the magnetic force pulling the liquid from the nozzle 11 is 3 X 'l0 dynes. With the nozzle outlet or orifice 12 having a diameter of two mils and the surface tension'being 40 dynes/cm, the force of the surface tension on the liquid is approximately 1.6 X 10 dynes. Thus, the magnetic force is comparable to the surface tension force so as tobe able to pull one of the droplets 19 from the outlet or orifice 12 of the nozzle 1 1 when the system is under slight positive pressure.

Referring to FIG. 2, there is shown another form of the present invention in which a magnet 25 is disposed on the opposite side of the paper from the nozzle 11. A plurality of windings of a coil 26 is wrapped around the magnet and has its ends connected to a pulse generator 27. Whenever the pulse generator 27 supplies a current to the coil 26, the magnet 25 creates a magnetic force to pull the droplet 19 from the outlet or orifice 12' of the nozzle 11.

With the magnet 25 disposed on the opposite side of the recording surface 20 from the outlet or orifice 12 of the nozzle 11, the magnetic force produced by the magnet 25 pulls the droplet 19 out of the outlet or orifice 12 of the nozzle 1 l for impingement on the recording surface 20. As described with respect to FIGS. 1A and 1B, the pulse generator 27 is activated in accordance with the pattern'and the rate of movement of the paper 20 to cause each of the droplets 19 to be pulled from the outlet or orifice 12 of the nozzle 11 when desired to form the desired pattern on the paper 20.

Referring to FIG. 3, there is shown another form of the present invention in which both of the magnets 14 and 25 are employed. In this arrangement, the coils 17 and 26 are connected to a single pulse generator 28.

. Thus, magnetic forces from the magnets 14 and 25 are no longer applied. Thus, the magnet 25 is turned on 6 after the droplet 19 is pulled from the outlet or orifice 12 of the nozzle 11 by the magnetic force from the magnet 14 and before the droplet 19 passes the change in force gradient that would tend to cause instability of the motion of the droplet 19.

Instead of using the single pulse generator 28, the coils 17 and 26 could be connected to the separate pulse generators 18 and 27, respectively. In such an arrangement, it would not be necessary to use the delay 29, but some means would have to be employed to insure that the pulse generator 27 causes the magnetic field from the magnet 25 to continue to be applied after the magnetic field from the magnet 14 is stopped so that a magnetic force is exerted on the droplet 19.

The magnet 14 provides a greater force to initially pull the droplet 19 from the outlet or orifice 12 of the nozzle 11 than the magnet 25 can produce by itself, and the magnet 25 insures that the droplet 19 is applied to the paper 20without the reverse force of the gradient producedby the magnet 14 having any effect on the motion of the droplet 19. Thus, the paper 20 does not need to be placed as close to the outlet or orifice 12 of the nozzle 11 as in the embodiment of FIG. 1A. However, a greater magnetic force can be applied directly adjacent the outlet or orifice 12 of the nozzle 11 for pulling the droplet 19 from the outlet ororifice 12 of the nozzle 1 1 than can be obtained from using only the embodiment of FIG. 2.

An advantage of this invention is that ink droplets can be asynchronously directed to a recording surface at a relatively high rate of speed. Another advantage of this invention is that there is no mechanical deformation of any structure so that there is no limitation on the rate of droplet formation insofar as resonant frequencies are concerned. 9

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of selectively causing asynchronous re moval of a droplet from a reservoir of a magnetic liquid for application to a recording surface including:

positioning the outlet of a reservoir of a magnetic liquid at a relatively low static pressure adjacent a recording surface on which droplets are to be impinged with the surface tension of the liquid preventing the magnetic liquid from escaping from the outlet; selectively applying a unidirectional magnetic force I extending from within the reservoir and at least through the outlet of the reservoir and prior to the recording surface in the direction toward the recording surface on the magnetic liquid to pull a droplet from the outlet of the reservoir for application to the recording surface whenever a droplet is to be applied to the recording surface; and disposing the recording surface so that its distance from the outlet of the reservoir enables the droplet to be applied to the recording surface by the unidirectional magnetic force.

2. A method of selectively causing asynchronous removal of a droplet from a reservoir of a magnetic liquid for application to a recording surface including:

positioning the outlet of a reservoir of a magnetic liquid at a relatively low static pressure adjacent a recording surface on which droplets are to be impinged with the surface tension of the liquid preventing the magnetic liquid from escaping from the outlet; selectively applying a unidirectional magnetic force extending from within the reservoir and at least through the outlet of the reservoir and prior to the recording surface in the direction toward the recording surface on the magnetic liquid to pull a droplet from the outlet of the reservoir for application to the recording surface whenever'a droplet is to be applied to the recording surface; and applying an additional magnetic force to the droplet from the opposite side of the recording surface to that on which the outlet is disposed with the additional magnetic force being applied in the same direction as the unidirectional magnetic force and in conjunction therewith to aid in applying the droplet to the recording surface. 3. The method according to claim 2 including continuing to apply an additional magnetic force after the unidirectional magnetic force is stopped.

4. An apparatus for asynchronously applying droplets of a magnetic liquid to a recording surface including:

means to store the magnetic liquid including an outlet disposed adjacent the recording surface, said storing means maintaining the magnetic liquid under a very low static pressure so that the surface tension of the magnetic liquid prevents the magnetic liquid from escaping from said outlet;

magnetic force producing means disposed adjacent said outlet and on the same side of the recording surface as said outlet to selectively apply a unidirectional magnetic force in the direction toward the recording surface on the magnetic liquid in said storing means and at least through said outlet to cause a droplet to be pulled from said outlet for application to the recording surface whenever a droplet is to be applied to the recording surface;

and said storing means having its outlet disposed sufficiently close to the recording surface so that the droplet can be applied to the recording surface by the unidirectional force of said magnetic force producing means.

5. The apparatus according to claim 4 in which the periphery of said outlet of said storing means is disposed within said magnetic force producing means.

6. The apparatus according to claim 4 in which said magnetic force producing means includes:

a magnet having a pair of tapered pole faces adjacent said outlet;

and means to selectively apply a unidirectional magnetic force from said magnet on the magnetic liquid in said storing means to pull a droplet from said outlet for application to the recording surface.

7. The apparatus according to claim 6 in which said outlet of said storing means is disposed between said tapered pole faces of said magnet.

8. The apparatus according to claim 6 in which said tapered pole faces of said magnet are tapered in the direction in which the droplet travels with the minimum gap between said tapered faces being closest to the recording surface.

9. The apparatus according to claim 8 in which said pole faces of said magnet have their tips disposed closer to the recording surface than the narrowest width of the gap between said pole faces.

10. The apparatus according to claim 8 in which said outlet of said storing means is disposed between said tapered pole faces of said magnet.

11. An apparatus for asynchronously applying droplets of a magnetic liquid to a recording surface including:

means to store the magnetic liquid including an outlet disposed adjacent the recording surface; said storing means maintaining the magnetic liquid under a very low static pressure so that the surface tension of the magnetic liquid prevents the magnetic liquid from escaping from said outlet;

first magnetic force producing means disposed adjacent said outlet and on the same side of the recording surface as said outlet to selectively apply a unidirectional magnetic force in the direction toward the recording surface on the magnetic liquid in said storing means and at least through said outlet to cause a droplet to be pulled from said outlet for application to the recording surface whenever a droplet is to be applied to the recording surface;

and second magnetic force producing means disposed on the opposite side of the recording surface from said outlet to apply an additional magnetic force on the magnetic liquid in the same direction as the unidirectional magnetic force of said first magnetic force producing means and in conjunction therewith to aid in applying the droplet to the recording surface.

12. The apparatus according to claim 11 including means to cause said second magnetic force producing means to continue to apply the additional magnetic force after said first magnetic force producing means is inactivated.

13. The apparatus according to claim 11 in which said second magnetic force producing means includes:

a magnet disposed on the opposite side of the recording surface from said outlet;

and means to selectively apply the additional magnetic force from said magnet on the magnetic liquid in said storing means in conjunction with and in the same direction as the unidirectional magnetic force from said first magnetic producing means to aid in applying the droplet to the recording surface.

14. The apparatus according to claim 10 in which said first magnetic force producing means includes a magnet having a pair of tapered pole faces adjacent said outlet 15. The apparatus according to claim 14 including means to cause said magnet of said second magnetic force producing means to continue to apply the additional magnetic force after said magnet of said first magnetic force producing means is inactivated. 

1. A method of selectively causing asynchronous removal of a droplet from a reservoir of a magnetic liquid for application to a recording surface including: positioning the outlet of a reservoir of a magnetic liquid at a relatively low static pressure adjacent a recording surface on which droplets are to be impinged with the surface tension of the liquid preventing the magnetic liquid from escaping from the outlet; selectively applying a unidirectional magnetic force extending from within the reservoir and at least through the outlet of the reservoir and prior to the recording surface in the direction toward the recording surface on the magnetic liquid to pull a droplet from the outlet of the reservoir for application to the recording surface whenever a droplet is to be applied to the recording surface; and disposing the recording surface so that its distance from the outlet of the reservoir enables the droplet to be applied to the recording surface by the unidirectional magnetic force.
 2. A method of selectively causing asynchronous removal of a droplet from a reservoir of a magnetic liquid for application to a recording surface including: positioning the outlet of a reservoir of a magnetic liquid at a relatively low static pressure adjacent a recording surface on which droplets are to be impinged with the surface tension of the liquid preventing the magnetic liquid from escaping from the outlet; selectively applying a unidirectional magnetic force extending from within the reservoir and at least through the outlet of the reservoir and prior to the recording surface in the direction toward the recording surface on the magnetic liquid to pull a droplet from the outlet of the reservoir for application to the recording surface whenever a droplet is to be applied to the recording surface; and applying an additional magnetic force to the droplet from the opposite side of the recording surface to that on which the outlet is disposed with the additional magnetic force being applied in the same direction as the unidirectional magnetic force and in conjunction therewith to aid in applying the droplet to the recording surface.
 3. The method according to claim 2 including continuing to apply an additional magnetic force after the unidirectional magnetic force is stopped.
 4. An apparatus for asynchronously applying droplets of a magnetic liquid to a recording surface including: means to store the magnetic liquid including an outlet disposed adjacent the recording surface, said storing means maintaining the magnetic liquid unDer a very low static pressure so that the surface tension of the magnetic liquid prevents the magnetic liquid from escaping from said outlet; magnetic force producing means disposed adjacent said outlet and on the same side of the recording surface as said outlet to selectively apply a unidirectional magnetic force in the direction toward the recording surface on the magnetic liquid in said storing means and at least through said outlet to cause a droplet to be pulled from said outlet for application to the recording surface whenever a droplet is to be applied to the recording surface; and said storing means having its outlet disposed sufficiently close to the recording surface so that the droplet can be applied to the recording surface by the unidirectional force of said magnetic force producing means.
 5. The apparatus according to claim 4 in which the periphery of said outlet of said storing means is disposed within said magnetic force producing means.
 6. The apparatus according to claim 4 in which said magnetic force producing means includes: a magnet having a pair of tapered pole faces adjacent said outlet; and means to selectively apply a unidirectional magnetic force from said magnet on the magnetic liquid in said storing means to pull a droplet from said outlet for application to the recording surface.
 7. The apparatus according to claim 6 in which said outlet of said storing means is disposed between said tapered pole faces of said magnet.
 8. The apparatus according to claim 6 in which said tapered pole faces of said magnet are tapered in the direction in which the droplet travels with the minimum gap between said tapered faces being closest to the recording surface.
 9. The apparatus according to claim 8 in which said pole faces of said magnet have their tips disposed closer to the recording surface than the narrowest width of the gap between said pole faces.
 10. The apparatus according to claim 8 in which said outlet of said storing means is disposed between said tapered pole faces of said magnet.
 11. An apparatus for asynchronously applying droplets of a magnetic liquid to a recording surface including: means to store the magnetic liquid including an outlet disposed adjacent the recording surface, said storing means maintaining the magnetic liquid under a very low static pressure so that the surface tension of the magnetic liquid prevents the magnetic liquid from escaping from said outlet; first magnetic force producing means disposed adjacent said outlet and on the same side of the recording surface as said outlet to selectively apply a unidirectional magnetic force in the direction toward the recording surface on the magnetic liquid in said storing means and at least through said outlet to cause a droplet to be pulled from said outlet for application to the recording surface whenever a droplet is to be applied to the recording surface; and second magnetic force producing means disposed on the opposite side of the recording surface from said outlet to apply an additional magnetic force on the magnetic liquid in the same direction as the unidirectional magnetic force of said first magnetic force producing means and in conjunction therewith to aid in applying the droplet to the recording surface.
 12. The apparatus according to claim 11 including means to cause said second magnetic force producing means to continue to apply the additional magnetic force after said first magnetic force producing means is inactivated.
 13. The apparatus according to claim 11 in which said second magnetic force producing means includes: a magnet disposed on the opposite side of the recording surface from said outlet; and means to selectively apply the additional magnetic force from said magnet on the magnetic liquid in said storing means in conjunction with and in the same direction as the unidirectional magnetic force from said first magnetic producing means to aid in applying the droplet to the recording suRface.
 14. The apparatus according to claim 10 in which said first magnetic force producing means includes a magnet having a pair of tapered pole faces adjacent said outlet
 15. The apparatus according to claim 14 including means to cause said magnet of said second magnetic force producing means to continue to apply the additional magnetic force after said magnet of said first magnetic force producing means is inactivated. 